As shown in FIG. 1, it is convenient to join pipe ends 10 and 12 with a mechanical pipe coupling 14. Pipe coupling 14 comprises oppositely disposed coupling portions 16 and 18 that are bolted circumferentially around pipe ends 10 and 12. A seal 20 is captured between the coupling portions and the pipe ends to effect a fluid-tight seal at the joint. As shown in FIG. 2, coupling portions 16 and 18 have arcuate keys 22 that engage circumferential grooves 24 formed in the pipe ends 10 and 12. When installed on the pipe ends with a seal 20, the keys 22 engage the grooves 24 to hold the pipes together and resist axial tension or compression forces, as well as bending moments to effect a reliable, fluid-tight joint between the pipe ends.
It is preferred to form the grooves 24 in the pipe ends by cold working the material between a grooving tool, such as a grooving roller, and a die, the grooving roller being applied to the outer surface of the pipe ends and the die supporting the inside pipe surface directly beneath the grooving roller. When the grooving roller is moved circumferentially around the pipe end and forced against the pipe surface, material is displaced predominately inwardly to form the groove 24, the die receiving the displaced material and forming a corresponding bump 26 on the inside pipe surface.
Forming grooves 24 by cold working the pipe material is preferred to cutting grooves, especially in marine applications where strength and corrosion are important considerations. Cold-worked grooves provide joints having increased corrosion allowance over cut grooves, but it is difficult to form such grooves in thick walled pipe, such as schedule 80 steel pipe. Currently, portable grooving machines are available that attach to the pipe wall and travel around the circumference of the pipe, forming the groove between an outer grooving roller and an inner die roller between which the pipe wall is compressed. Such machines are difficult to control and fatiguing to the operators. Further, they are limited in the amount of force they can effectively apply without producing undue pipe diameter growth and flare, which limits the diameter and wall thickness of the pipes with which they can be used.
Another type of prior art grooving apparatus rotates the pipe relatively to the apparatus. However, it is both difficult and unsafe to form grooves in pipe assemblies or curved pipe segments (known as “bent pipe spools”) using such apparatus. Furthermore, even when straight pipe is grooved, pipe stands are necessary to support the pipe as it is rotating and being grooved. It is difficult when using pipe stands to establish and maintain the alignment of the pipe with the grooving apparatus. Proper alignment between the pipe and grooving apparatus is needed to ensure formation of a circumferential groove.
Moreover, prior art grooving apparatus of both types (orbital and rotating) control the dimensions of the groove measuring from the pipe internal surface to the grooved surface. The dimensions of grooves formed by such apparatus are adversely affected by variations in the pipe outer diameter tolerance as well as the tolerances of the pipe wall thickness. The accuracy of the groove dimensions is, thus, dependent on the dimensions of the pipe and will vary in proportion to the variation in pipe dimensions. It is, thus, difficult to attain a desired level of consistency and repeatability in the formation of grooves to ensure quality pipe joints.
In view of the drawbacks associated with prior art grooving apparatus, there is clearly a need for an improved grooving tool that can form grooves in thick walled pipe, pipe assemblies and curved pipe segments conveniently, safely, with repeatability, accuracy and with less operator fatigue.